The present invention relates to a shift member and more particularly to a heat-resistant shift member, and also relates to a method for manufacturing the same.
Here the term "heat-resistant shift member" used throughout the present Specification and claims should be interpreted to designate an element which can carry a load with a low coefficient of friction even under temperatures in which the application of generally used lubricant oils is difficult and additionally has a sealing function, i.e. as a sealing element to be used at elevated temperatures, e.g. a bearing bush, a washer, a sliding board, a contact type packing or the like.
Hitherto, as a shift member of this kind or metallic member made of stainless steel, copper alloy within which are embedded pellets of a solid lubricant, a non-metallic material made of graphite, ceramics, etc., a compound material such as the so-called "cermet", heat-resistant plastic material such as polytetrafluoroethylene (PTFE), polyamid, etc. have been publicly known.
However, although these materials are all excellent in heat resistance, they have problems in friction and wear under dry friction conditions and difficulties in mechanical strength, in particular shock impact resistance, not necessarily having good conformability with the counter member, and cannot fulfill those functions sufficiently in the case of minute sliding.
In order to solve these difficulties or problems, as disclosed in e.g. U.S. Pat. No. 1,137,373, Japanese Patent Publication No. 23966/1969, etc. a shift member has already been developed wherein expanded graphite obtainable by a special treatment of graphite is shaped in association with a reinforcing member. Although these publicly known shift members have good heat resistance revealing superiority in conformability with the counter member and have improved shock impact resistance compared with regular graphite, the coefficient of friction is rather somewhat higher than that of regular graphite and they have a defect in that they after generate abnormal frictional sounds at the time of shifting under dry friction conditions.
Further a shift member which is produced by similarly shaping a heat-resistant material such as mica, asbestos, etc. together with reinforcing materials has also been publicly known, but it has problems similar to those in the above described shift members.
The reasons why therefor, are considered to reside in the fact that these shift members have large differences in friction coefficients between their static and dynamic friction, and they have a certain extent of flexibility, and also it is considered that the shapes and the natural frequencies of the various components constituting the slip system has an effect on those phenomenon.